1. Field of the Invention
The present invention relates, in general, to the field of precision ranging instruments. More particularly, the present invention relates to an apparatus and method for utilizing a light based speed and/or range finder apparatus to determine absolute reflectivity of reflective objects such as highway directional and informational signs.
2. Description of Related Art
Retroreflective sheeting is commonly used to provide reflective informational signs along highways, on roadways and on safety barriers along roadways. For example, stop signs, caution signs and highway directional signs often have such sheeting materials or coatings to enhance the visibility of the signs and especially the lettering to motorists traveling at night.
The only illumination of these signs is provided by the oncoming vehicle headlights. The retroreflective sheeting suffers from the disadvantage that its reflectivity deteriorates with age and exposure to the environmental effects of sun, wind, and precipitation. These signs must therefore be periodically inspected, refurbished and/or replaced. Anticipated state and/or federal government regulations for reflectivity of road signs may soon require that periodic measurements of sign reflectance or more frequent sign replacements be undertaken to meet reflectivity standards.
It is currently extremely difficult to accurately measure reflectivity of such signs along roadways in the field. Measurements of a sign's reflectivity require very precise instrument locations close to the sign, precise lighting conditions, and often require either sign removal or closure of the highway portion immediately in front of the sign while the required lighting and sensing instruments are set up and measurements taken. Such road closures or driving restrictions placed on motorists are inconvenient and generate a safety concern not only for the instrument operators taking measurements, but also to motorists in the vicinity. Currently, a sign must be relocated to a test facility where a light source and suitable filters may be accurately positioned in order to perform the measurements. Alternatively, the test setup may be implemented at the sign location, but such field measurements are prone to errors which may be unacceptable to meet new standards which may be forthcoming. Consequently, there is a need for a convenient and safe method for remotely ascertaining absolute reflectivity of a sign surface.
Another problem is that the reflectivity of many signs deteriorates nonuniformly. Portions of the sign which receive more direct sunlight or are colored with more light sensitive paint materials deteriorates faster than other portions. Consequently, accurate determinations of sign reflectivity are difficult to make and reflectivity determinations of important portions of the sign, such as the letters and numbers, as opposed to background portions, may be highly inaccurate. Therefore there is a need for a method of accurate reflectivity determinations for selected portions of signs rather than the entire sign.